Lead collision track and scan system



Allg- 1963 R. G. SHELLEY 3,102,262

LEAD COLLISION TRACK AND SCAN SYSTEM Filed Feb. 1, 1957 2 Sheets-Sheet i COLLISION HEADING PIC-3.6

l 0 Z (I 20 O f l sms AZIMUTHANGLE INVENTOR. RULON G. SHELLEY am &%

ATTORNEY Aug. 27, 1963 Filed Feb. 1. 1957 R- G. SHELLEY LEAD COLLISION TRACK AND SCAN SYSTEM 2 Sheets-Sheet 2 27 PHASE SENSITIVE DEMODULATOR RESPONSE GENERATOR 29 GYRO 2' SYNC i2 ER T H m E GA ms COMPASS 225 3| SWITCHING 32 RADAR s EIEE 411 38 GENERATOR as 33 PHASE 39 SENSITIVE DEMODULAT 35 r' I FIG.4

VERT. SWEEP 5| I::| [:1 we

' 52 E n [1 LEAD COLLISION CURSOR Fla 5 INVENTOR.

RULON G. SHELLEY ATTORNEY United States Patent 3,102,262 LEAD COLLISION TRACK AND SCAN SYSTEM Rulon G. Shelley, Downey, Califl, assignor to North American Aviation, inc. Filed Feb. 1, 1957, Ser. No. 637,729 12 Claims. (Cl. 343-7) This invention relates to track and scan systems and more particularly to apparatus for providing the operator of an attacking vehicle such as an interceptor aircraft with means for obtaining a suitable approach course while simultaneously scanning in and about a target area.

Present lead pursuit systems provide a pursuit type approach course which ends upon the tail of the target or else are g limited (limited by the maneuverability of the aircraft) or beyond firing range. A tail chase is undesirable when attacking a target which carries tail armament. Further, the interceptor would be better able to say out of the target jet Wash and the kill probably would be increased if, at the time of firing or at the time of initiation of a lead pursuit course, the interceptor could be positioned at a greater angle off the tail of the target.

The present invention provides the interceptor pilot with means for obtaining a straight line approach course that terminates tangent to a lead pursuit path, thus placing the interceptor in a more favorable position to com plete the attack. Such an approach course is a lead col- -lision course. In accordance with the invention, the interceptor pilot is provided with a display of the range and bearing of the target relative to the interceptor and its heading. There is generated a signal which is indicative of the lead collision angle, defined as the angle between the line of sight from the interceptor to the target and a line from the interceptor which lies along the lead collision path. This signal is utilized to provide a bearing cursor on the display which when superimposed upon the displayed target indicates the desired lead collision course. By suitable azimuth maneuver of the interceptor, the pilot will maintain coincidence of target and cursor to keep the interceptor on the lead collision course.

It is an object of this invention to improve the tracking of a moving target.

A further object of this invention is to track a moving target while simultaneously scanning an area in and about the target.

Another object of this invention is to obtain an improved approach course.

A further object is the provision of apparatus for enabling a pilot to maintain a lead collision approach course.

These and other objects of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

FIGS. 1 and 2 illustrate attack geometry;

FIG. 3 illustrates a typical display obtained with the apparatus of the present invention;

FIG. 4 comprises a schematic illustration of the electrical components of a preferred embodiment of the invention;

FIG. 5 is a timing chart of the wave forms which exist in the apparatus of FIG. 4; and

FIG. 6 illustrates the circuitry of one form of response generator.

For a brief discussion of attack geometry reference is made to FIGS. 1 and 2, wherein an interceptor aircraft located at point 10 is attacking a target located at point 11 and headed in the direction of the line 11-42.

The symbols used in FIGS. 1 and 2 are defined as follows:

G represents the angle between target heading and the line of sight from interceptor to target.

sine H= sine G (1) For a pure collision course TK=VIT and the collision lead angle H may be defined as sine H sine G (3) The lead collision geometry is illustrated in FIG. 2 and defines a course which will bring about collision of the interceptors missiles with the target rather than collision between the interceptor itself with the target as in the pure collision course. With the interceptor and target initially at points 13 and 14 respectively, the interceptor will fire its rocket or other missiles when it is at point 15 at which time the target is at point 16. The target then travels a distance of V T to point 17 where it meets the fired missile. At the time of collision between target and missile, the interceptor is at point 18. Since the missiles are fired along the interceptor heading, it will be seen that when the interceptor is at point 18, the lead angle is zero since the interceptor is now headed directly at the target and the target range is V T Thus for the lead collision course For a long initial range V T, the lead collision angle H and the collision angle H are substantially equal,

it can be shown that the equation relating the lead collision angle to the collision angle is For a collision course, it is known that the rate of rotation in inertial space of the line of sight from the interceptor to the target is zero. Since the approach problem is mainly one of azimuth only and along the earths surface a suitable criterion for a collision approach course is a constant azimuth angle between the line of sight from the interceptor to the target and the line from the interceptor in a fixed spatial direction such as magnetic north. Thus a collision course cursor may be displayed on a B type radar presentation for example, by initially superimposing a bearing cursor upon the displayed target and causing such cursor to move relative to the: interceptor sineH =sine H sine G sine (H H C)= sine H G heading in accordance with the relative rotation of the interceptor heading and magnetic north. However, since the collision approach course does not put the attacking airplane near a firing position, it is more desirable to provide a cursor which indicates a lead collision course to enable the interceptor to fly a straight line course that terminates tangent to a lead pursuit path in a position to complete the attack. The characteristics of such a lead collision course are that at long ranges the rate of rotation in inertial space of the line of sight from the interceptor to the target approaches zero, i.e., the lead collision and collision paths are essentially the same at long range as indicated by Equation 7. As range decreases, the rate of rotation of the line of sight to the target increases for the lead collision course thus decreasing the lead angle which, as pointed out above, becomes zero at the nominal relative firing distance, V T

In accordance with the invention, there is generated a reference signal continuously indicative of the heading of the interceptor relative to a fixed spatial direction and a bias signal is added to this reference signal to produce a collision course signal. The collision course signal H is fed to a response generator which substantially computes the lead collision angle H in accordance with Equation 8. The output of this response generator is plotted against range from the interceptor to provide the lead collision cursor. The display thus provided will appear as indicated in FIG. 3 and comprises the target trace -19 and the lead collision cursor 20 together with such other targets that may be within the scanning field of the radar.

Referring now to FIG. 4, a gyro compass 21 may in clude a suitable position indicating synchro which provides a shaft rotation output proportional to the angle between interceptor heading and a fixed spatial direction such as magnetic north. This angle may be the aircraft azimuth heading. This shaft rotation output is applied to rotor coils 22 which are energized at some suitable frequency such as for example, 400 cycles per second, by source 23' and stator coil 24. A bias angle may be added to the gyro compass derived angle by a manual control 25 connected to rotate rotor coil 26 which is energized from rotor 22 through stator coils 23. The signal thus induced in rotor 26 alternates at the frequency of source 23' and has -a magnitude directly proportional to the sine of the diiference or algebraic sum of the gyro compass derived angle and the manually derived bias angle. This signal is fed to a phase sensitive demodulator 27 which produces a direct current output of a polarity and magnitude in accordance with the phase and magnitude of the signal in rotor 26. Thus the output of the phase sensitive demodulator is proportional to sine H the collision lead angle. The signal sine H is fed to response generator 28 more particularly described hereinafter which substantially computes the lead collision angle sine H The radar system itself is substantially conventional and comprises synchronizer 29 which produces the synch pulses '30 which control the repetition rate of the pulses transmitted by the radar 31 and of the vertical sweep voltage 32 produced by the vertical sweep generator 33. A horizontal deflection voltage proportional to the sine of the bearing of the radar antenna relative to the aircraft heading is obtained from a phase sensitive demodulator 34 which is energized from alternating current source 35 and stator coil 36 through rotor coil 37 which is physically positioned by an angular position signal derived from the radar 31. The position signal from the radar is directly proportional to the antenna bearing angle. This direct current signal from demodulator 34, proportional to the sine of the antenna bearing, is fed through the switching or time-sharing circuit 38 to the horizontal deflection controls of display device or cathode ray tube 39' together with the vertical sweep voltage 32 which is fed to the vertical deflection controls of the display device. Thus the cathode ray of the tube 39 is caused to move over the display area or screen of the tube is accordance with the angular antenna position and a predetermined time base indicative of range. Echoes of pulses transmitted by the radar and reflected from a target are received by the radar and fed to the intensity controls of the cathode ray tube whereby there is produced a B scan display indicating target range in accordance with the vertical deflection of the display point 19 (FIG. 3). The display also indicates the sine of the target azimuth angle relative to the interceptor heading as indicated by the horizontal deflection of the display point 19. Thus with the switching device or circuit 38 in position to feed the antenna bearing signal to the tube 39, the apparatus will provide for the scanning of the area within an angle such as, for example, to either side of the aircraft heading. With the switchin g circuit 38 disposed to couple the output of the response generator 38 to the horizontal deflection control of tube 39, the vertical sweep signal is fed, as above, to the vertical deflection controls and the cathode ray of the tube is horizontally displaced in accordance with magnitude of the sine of the lead collision angle. Thus the lead collision angle is plotted on the screen as a function of range from the interceptor to produce the lead collision cursor 20. Gating circuit 50, timed from synchronizer 29, generates a gating signal 51 which is delayed from the start of the vertical sweep by a predetermined time which may be proportional to VoTf range as indicated in FIG. 5. The switching circuit 38 eflects the time sharing of the lead collision cursor with the antenna bearing signal whereby there is simultaneously (due to screen persistence) displayed results of the antenna search of the target area and the azimuth cursor which enables the pilot to maintain the lead collision approach course as will presently be described.

It will be readily appreciated that the invention could be implemented by means of a multiple gun oscilloscope thus eliminating the need for switching circuit 38. With such a multiple gun arrangement the cursor and vertical sweep might be put on one gun while the target and search information would be on another.

Assume the pilot has acquired a target on the B scope display during normal scanning operation at or near maximum range. The cursor 20 is now appearing on the screen or at this time a suitable switch may be operated to cause the azimuth cursor to be timed-shared with the search display. Manual control 25 is then actuated by the pilot to generate the bias signal indicative of the angle between a spatial reference line (the magnetic north detected by the gyro compass) and a line between the target and the interceptor. This is actually effected by turning the knob 25 until the crustor 20 is shifted horizontally to be positioned directly over the target. It is then necessary for the pilot to maneuver and fly the interceptor so as to keep the target azimuth rate or drift relative to the collision trace zero. In effect the pilot has established the collision angle H which at this long range is substantially equal to the lead collision angle H The pilot maneuvers the aircraft so as to maintain the target superimposed upon the azimuth cursor. If the pilot has estalblished the proper course, the target will continue to move down the lead collision trace and this maneuver is continued until the display indicates to the pilot that a suitable firing range has been reached or that a range suitable for initiating a lead pursuit path has been reached. If the target appears to drift with respect to the trace, a change in heading of the aircraft is required until the drift is again zero. The hand control 25 would then be adjusted slightly to again superimpose the cursor on the target if lateral displacement had occurred. This procedure will result in a proper lead collision approach course to the firing range. It will be seen, therefore, that the juxtaposition or superposition of the lead collision cursor on the target by the display device in effect compares the target bearing with the lead collision angle at substantially all target ranges.

It can be shown that the lead collision trace indicated by Equation 8, the variation of the lead collision angle with collision angle, can be substantially matched by an exponential of the following form This exponential curve may be substantially duplicated by the response to a step input in sine H delayed 2.03l V T seconds, of a network which has the transfer function of sine HLC sine HQ where T T and T are predetermined values given in real time as indicated below and S represents the complex operator indicating the operation of differentiation. However, the actual values required will be determined by the vertical sweep rate used on the display tube.

A network having the transfer function defined in Equation 10 is indicated in FIG. 6 and comprises a resistor 60 having one end thereof coupled to ground through a pair of parallel paths comprising resistor 61, capacitor 62 and capacitor 63. The input to the circuit from the phase sensitive demodulator 27 (FIG. 4) is at terminal 64 while the output thereof is derived at terminal 65 which comprises the junction of elements 60, 61 and 63. The gating signal 51 may be fed to the junction between the cathode of diode 66, which has its anode connected to terminal 64, and resistor 67 which is connected to a suitable source of negative potential. Thus in the absence of the gating signal, the diode clamps terminal 64 to a relatively low potential which may be ground while the positive gating signal will cut off the diode and allow the collision signal H to be fed to the response generator 28.

Exemplary component values of the circuit of FIG. 6 which will provide an output H closely approximating the value thereof given in Equation 8 are as follows: For an assumed value of V T equal to 5,000 feet.

Resistor 60'=200.6 ohms Resistor 61: 1,000 ohms Capacitor 62:.055 microfarad Capacitor 63:.0415 microfarad These values define the constants T T and T of Equation 10 and the latter becomes sine H LC sine H c It is to be understood that the invention is not to be limited to the specific circuitry or values thereof which have been disclosed since the desired response, H or sine H may readily be obtained by other circuits or components of other values as will readily be apparent to those skilled in the art.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. Tracking apparatus comprising means for deriving the range of a moving target relative to an attacking aircraft and the target bearing, means for deriving the lead collision angle of said aircraft relative to said target as a function of target range, and means for presenting said angle for comparison with said hearing at varying ranges.

2. A tracking system comprising means for obtaining the range and bearing of a moving target with respect to an approaching vehicle and its heading, means for generating a signal representative of collision angle of said vehicle relative to said target, response means coupled with said generating means for providing a course signal representative of lead collision angle of said vehicle, and means for presenting said course signal for comparison with said range and bearing.

3. A tracking system comprising means for obtaining the range and bearing of a moving target. with respect to an approaching vehicle and its heading, means for generating a signal representative of collision angle of said vehicle relative to said target, response generator means responsive to said signal for providing a recurring and delayed step function of said signal, said step function comprising a lead collision course signal having a substantially exponential rise, and means for presenting said lead collision course signal for comparison with said range and bearing.

4. A track and search system comprising a display device having a display area and means for producing a display point on said area, first deflection means including a sweep generator for controlling the position of said display point in a first direction on said area, radar means for generating range and bearing signals, means responsive to said range signal for intensity modulating said display point, second deflection means for controlling the position of said display point in a second direction on said area, means for generating a collision signal indicative of the angle between the heading of an attacking aircraft and a spatial reference line, means for generating a lead collision course signal as a function of said collision'signal, and means for alternatively feeding said bearing signal and said lead collision course signal to said second deflection means.

5. A track and scan system comprising radar means for producing a display of the range and bearing of a moving target relative to an attacking aircraft and the heading thereof, means for generating a reference signal continuously indicative of the heading of said aircraft relative to a fixed spatial line, means for generating a bias signal indicative of the angle between said spatial line and a line between said target and aircraft at rela tively long target range, means for combining said reference and bias signals to produce a collision course signal indicative of the collision angle between the heading of said aircraft and a spatial reference direction, means for generating a lead collision course signal as a function of said collision course signal and decreasing with de creasing range, and means responsive to said lead collision course signal for producing an azimuth cursor on said display.

6. A tracking system for indicating a lead collision approach course of an attacking aircraft comprising gyro compass means 'for generating a signal proportional to the azimuth heading of said aircraft relative to a spatial direction, means for generating a bias signal proportional to the angle between said spatial direction and the line of sight from said aircraft to a target at relatively long target range, means 'for generating a collision course signal proportional to the sine of the algebraic sum of said angle and said azimuth heading, a lead collision circuit having a transfer function defined by T S+1 m where T T and T are predetermined values, means for repetitively feeding said collision course signal to said circuit, and means for indicating the output of said circuit as a function of range from said aircraft.

7. The system of claim 6 including means for superposing on said indication of the output of said circuit an sine H c where V T; is a predetermined distance and r is the range of said target from said aircraft, and means responsive to said course means for plotting said angle H as a function of said range r.

9. A track and search system comprising a display device having a display area and means for producing a sine (H H display point on said area, first deflection means including a sweep generator for controlling the position of said display point in a first direction on said area, radar means for generating range and bearing signals, means responsive to said range signal for intensity modulating said display point, second deflection means for controlling the position of said display point in a second direction on said area, means for generating a collision signal indi cative of the angle between the heading of an attacking aircraft and a spatial reference line, circuit means responsive to said collision signal generating means for computing a course signal indicative of the lead collision angle between the heading of said aircraft and a line therefrom to a target, and means for alternatively feeding said bearing signal and said course signal to said second deflection means.

10. A track and scan system comprising radar means for producing a B scan display of the range and bearing of a moving target relative to an attacking aircraft and the heading thereof, means for generating a reference signal continuously indicative of the heading of said aircraft relative to a fixed spatial line, means for generating a bias signal indicative of the angle between said spatial line and a line between said target and aircraft at relatively long target range, means for combining said reference and bias signals to produce a course signal indicative of the collision angle between the heading of said aircraft and a spatial reference direction, computer means responsive to said combining means for generating a signal substantially proportional to the lead collision angle between said aircraft heading and a line from said aircraft to said target, and means responsive to said computer means for producing an azimuth cursor on said display.

11. A track andscan system comprising radar means for generating range and bearing signals indicative of range and bearing of a moving target relative to an attacking aircraft and its heading respectively, a gyro compass having a shaft output proportional to the azimuth heading of said aircraft, a rotor coil connected to be driven by said shaft output, means for energizing said rotor coil, a second rotor coil, means for manually driving said second'coil, means for energizing said second coil from saidfirst rotor coil, a lead collision angle com- .puter, a gating circuit synchronized from said radar ineans, means responsive to said gating means for repeti- Itively feeding the output of said second coil to said computer, said radar means including means for displaying said range and bearing signals, and means synchronized from said radar means for plotting the output of said computer on said display means as a function of range from said aircraft.

12. The system of claim 11 wherein said lead collision angle computer comprises a first resistor, one end of said resistor comprising an input terminal to said computer, a series connected capacitor and resistor connected between the other end of said first resistor and a fixed potential level, and a second capacitor connected across said series connected capacitor and resistor, said other end of said first resistor comprising an output terminal of said computer.

References Cited in the file of this patent UNITED STATES PATENTS 2,737,652 White et a1. Mar. 6, 1956 2,858,533 Richmond Oct. 28, 1958 2,879,502 Miller Mar. 24, 1959 

1. TRACKING APPARATUS COMPRISING MEANS FOR DERIVING THE RANGE OF A MOVING TARGET RELATIVE TO AN ATTACKING AIRCRAFT AND THE TARGET BEARING, MEANS FOR DERIVING THE LEAD COLLISION ANGLE OF SAID AIRCRAFT RELATIVE TO SAID TARGET AS A FUNCTION OF TARGET RANGE, AND MEANS FOR PRESENTING SAID ANGLE FOR COMPARISON WITH SAID BEARING AT VARYING RANGES. 